REALTIME CONTROL
RV229 Anemometer Adapter
Users Manual
8. Site evaluation using speed and direction distributions


The "Guided Tour on Wind Energy" from the Danish Wind Turbine Manufacturers Association includes information on wind power site evaluation.


The RV229 log file comprises a header followed by four blocks of distribution data.

The header contains diagnostic information.

The first block contains the wind speed distribution data necessary to calculate the total power which would have been generated by a particular turbine during the logged period, essential information for any economic analysis.

The remaining three blocks together contain the wind direction distribution data necessary to draw a wind rose, a useful tool for siting individual turbines within a landscape.

Each of the four blocks containing the distribution data begins with two lines which define the data in the block. When the log file is loaded into a spreadsheet program as a .csv file, these definitions will appear in the same columns as the data items to which they relate.


8.1 Header

Header example:

RV229 1.0,2259846338-164

The header comprises:
- the identifier, ie.  RV229
- the firmware version, eg. 1.0
- a comma separator
- the linearising coefficient for the transducer, eg. 2259846338
- a hyphen separator
- the optoelectronic threshold of the transducer, eg. 164

The header is useful to Realtime Control for diagnostics in the event of malfunction, and will generally be of little interest to the user.


8.2 Wind speed block

This block records the number of ten minute samples during which the average wind speed was within each of the nominated speed ranges.

There are 52 speed ranges in this block. The first 51 speed ranges, from 0 through 25.5 m/s, are 0.5 m/s wide. The final range covers 25.5 to 50 m/s.

Wind speed block example:

From,To,
m/s,m/s,#
0.0,0.5,233
0.5,1.0,418
1.0,1.5,922
.
.
.
24.5,25.0,9
25.0,25.5,6
25.5,50,1

Each sample covers a ten minute period, so the logged period in hours is the total number of samples divided by six.

In the example above, there were 233 samples during which the average wind speed was in the range 0.0 to 0.5 m/s, 418 samples during  which the average wind speed was in the range 0.5 to 1.0 m/s, and 1 sample during which the average wind speed was in the range 25.5 to 50 m/s.

This block can be used along with a turbine's power curve to calculate the total power which would have been generated during the logged period.
For each wind speed range, multiply the number of samples during which the wind speed was in that range by the turbine power output in kilowatts at the mid point of that speed range, then divide by six. The sum of all these is then the total power in kWh which would have been generated by that turbine during the logged period.


8.3 Wind direction block

This block records the number of ten minute samples during which the wind came from each of the sixteen 22.5 degree wide direction sectors.

Wind direction block example:

From,To,
deg,deg,#
0.0,22.5,153
22.5,45.0,121
45.0,67.5,47
.
.
.
292.5,315.0,263
315.0,337.5,948
337.5,360.0,324

In the example above, there were 153 samples during which the wind direction was between 0 and 22.5 degrees, 121 samples during  which the wind direction was between 22.5 and 45 degrees, and 47 samples during which the wind direction was between 45 and 67.5 degrees.


8.4 Distance run block

This block records the sums of the wind speed samples for each of the sixteen 22.5 degree wide direction sectors, and so contains figures proportional to the distance run by the wind in each sector.

Distance run block example:

From,To,Sum
deg,deg,m/s
0.0,22.5,9978
22.5,45.0,14332
45.0,67.5,5637
.
.
.
292.5,315.0,3326
315.0,337.5,6558
337.5,360.0,8709

In the example above, the sum of the wind speeds of all samples for which the wind direction was between 0 and 22.5 degrees was 9978.


8.5 Wind power block

This block records the sums of the cubes of the wind speed samples for each of the sixteen 22.5 degree wide direction sectors, and so contains figures proportional to the wind power in each sector.

Wind power block example:

From,To,Sum
deg,deg,(m/s)^3
0.0,22.5,3445287
22.5,45.0,12335976
45.0,67.5,8499622
.
.
.
292.5,315.0,4834743
315.0,337.5,34567554
337.5,360.0,74575478

In the example above, the sum of the cubes of the wind speeds of all samples during which the wind direction was between 0 and 22.5 degrees was 3445287.


8.6 Example of measurement and logging a wind speed and direction sample

This section follows the process of logging of a sample during a ten minute logging cycle.
Example values are included.

Time
 Action description
 Example values
0
 Sensor is depowered.
Wind Speed Total ("WST") is zeroed.

     
WST = 0
1 minutes 45 seconds
 Sensor is powered up.
2 minutes
 Wind speed is measured.
Wind speed is rounded up or down to the nearest 0.5 m/s.
Rounded wind speed is added to WST.
Sensor is depowered.

 5.3 m/s
5.5 m/s
WST=5.5
3 minutes 45 seconds
 Sensor is powered up.
4 minutes
 Wind speed is measured.
Wind speed is rounded up or down to the nearest 0.5 m/s.
Rounded wind speed is added to WST.
Sensor is depowered.

 5.7 m/s
5.5 m/s
WST=11
5 minutes 45 seconds
 Sensor is powered up.
6 minutes
 Wind speed is measured.
Wind speed is rounded up or down to the nearest 0.5 m/s.
Rounded wind speed is added to WST.
Wind direction is measured, and this value saved and used
during log updating at time = 10 minutes.
Sensor is depowered.

 5.0 m/s
5 m/s
WST=16

D(6)=224 degrees
7 minutes 45 seconds
 Sensor is powered up.
8 minutes
 Wind speed is measured.
Wind speed is rounded up or down to the nearest 0.5 m/s.
Rounded wind speed is added to WST.
Sensor is depowered.

 5.8 m/s
6.0 m/s
WST=22
9 minutes 45 seconds
 Sensor is powered up.
10 minutes Wind speed is measured.
Wind speed is rounded up or down to the nearest 0.5 m/s.
Rounded wind speed is added to WST.

 6.4 m/s
6.5 m/s
WST=28.5

WST is divided by 5 to give the average wind speed S(avg).

 S(avg)=5.7 m/s

Sensor is depowered.

In the Wind Speed block, the count in the range containing S(avg) is increased by 1.

 5.5 - 6.0 m/s count
is increased by 1

In the Wind Direction block, the count in the sector containing D(6) is increased by 1.

 202.5 - 225 degree sector count is increased by 1.

Average wind speed S(avg) is rounded up or down to the nearest .5 m/s

 S(avg. rounded)=5.5 m/s

In the  Distance Run block, the count in the sector containing D(6) is increased by S(avg. rounded).

 202.5 - 225 degree
sector is increased by 5.5.

In the Wind Power block the count in the sector containing D(6) is increased by S(avg.rounded) cubed. 202.5 - 225 degree
sector is increased by 166.375



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